One example of an inertial sensor the present inventors take into consideration is shown in FIG. 19. In this inertial sensor, a mass 500 is fixed to a basement layer by supports 503 via beams 501, 502. The mass 500 is vibrated in the X-direction by driving means 504, and when an angular rate about Z-axis or acceleration in the Y direction is applied, displaced also in the Y direction. This displacement in the Y-direction is detected by detection means 505 as an applied angular rate or acceleration.
In driving means 504 of this type of inertial sensor, fixed electrodes and movable electrodes thereof are disposed so that combs are meshed, electrostatic attractions are generated alternately between the fixed electrodes and movable electrodes by application of a DC bias voltage as well as an AC drive signals between the fixed electrodes and the movable electrodes, and then the mass 500 is brought in vibration.
Furthermore, in detection means 505, fixed electrodes and movable electrodes thereof are disposed so that combs are meshed, and the displacements of the mass 500 are detected as the change of an electrostatic capacity, whereby detection signals based on angular rates or accelerations are output.
Herein, an enlarged diagram of a region RA in driving means 504 of the inertial sensor of FIG. 19 is shown in FIG. 20. In this art, since the mass 500 is vibrated also in the Y direction which is a detection direction while being vibrated in the X direction which is a driving direction, the combs of driving means 504 are vibrated in a track b which is a composition of an amplitude dr in the driving direction and an amplitude de in the detection direction. In this case, a distance d and a distance s of the fixed combs and moving combs that form driving means 504 and detection means 505 are required to be disposed at a distance of not less than a drive displacement and a detection displacement.
Further, a previously known angular rate sensor based on, for example, the specification of Japanese Patent No. 3077077 (Patent Document 1), is an angular rate sensor referred to as a tuning-fork typed sensor, and is constructed such that, by causing a pair of masses located on a basement layer to vibrate in inverted phases to each other, vibrations transmitted from the masses to the basement layer via support beams are mutually cancelled with a pair of masses.
Moreover, an angular rate sensor described in, for example, U.S. Pat. No. 6,691,571 (Patent Document 2) is formed of three elements of a drive frame, a Coriolis frame, and a detection frame. In this angular rate sensor, a drive frame is supported by beams that are flexible in a driving direction, and rigid in a detection direction, and is structured to be easy to move in the driving direction, and hard to move in the detection direction. Furthermore, a detection frame is likewise supported to be easy to move in the detection direction, and an excitation and a detection vibration can be divided. In this case, although the detection frame is connected to a basement layer at two points via beams that are rigid in the driving direction and flexible in the detection direction, these beams, since they are formed in a narrow space, are in a complicated configuration having plural bends.
Furthermore, a previously known angular rate sensor, based on, for example, “Design, Simulation, and Implementation of Two Novel Micromechanical Vibratory-Rate Gyroscopes”, master's thesis of USA Carnegie Mellon University, published in May, 1998, (non-Patent Document 1), is formed of a drive frame, a Coriolis frame and a detection frame, and is structured such that the drive frame is supported by beams that are flexible in a driving direction and rigid in a detection direction, to be easy to move in the driving direction and hard to move in the detection direction. In addition, likewise a detection frame is supported to be easy to move in a detection direction, and is in such structure that excitation and a detection vibration are not coupled.
Further, a previously known angular rate sensor based on, for example, the specification of Japanese Patent No. 3589182, is comprised of not less than three masses disposed in alignment in a first axial direction, and vibrated in inverted phases one another in a second axis extending orthogonally to the first axis, and support beams that are extended in the first axial direction and that provide connections between these masses so as to be capable of displaced in the second axial direction. Further, this angular rate sensor is fixed to a basement layer at joints resided between these masses, and detects displacements generated by Coriolis force in the first axial direction. In this case, since suspensions including the masses are suspended with the joints, there is no leakage of excitation energy.
Further, by the simple combination of an angular rate sensor described in the above-mentioned Japanese Patent Application Laid-Open No. 2004-518969 and an angular rate sensor described in the above-mentioned Japanese Patent No. 3589182, an inertial sensor according to the present invention cannot be constructed.